1. Field of the Invention
The present invention relates to a method and apparatus for controlling at least one actuator in the drive train of a motor vehicle, especially a motor vehicle that is equipped with an automated twin-clutch transmission.
2. Description of the Related Art
Automated drive trains in which the clutch and/or the transmission are actuated by actuators in accordance with predetermined programs are increasingly used in passenger cars. Such transmissions not only increase driving comfort, but also enable considerable improvements in fuel consumption at low speed operation.
A portion of a drive train of such a vehicle is illustrated in FIG. 1a. 
A twin-clutch transmission, also called a parallel shift transmission, which has been generally designated with the reference numeral 10, includes two input shafts 12 and 14, each of which can be connected via a clutch 16 and 18, respectively, to the crankshaft 20 of an internal combustion engine. Arranged on the input shafts 12 and 14 are gears that can mesh with gears that are displaceably and non-rotatably arranged on an output shaft 15 for the purpose of shifting different gears.
An actuator 24 and 26 is associated with each clutch 16 and 18, respectively, for the actuation thereof.
The actuation arrangement for actuator 26 is shown in greater detail and includes an electric motor 30, the output pinion 32 of which includes an internal thread, which meshes with a threaded rod 34 that simultaneously acts as the rod of a piston 36 that operates in a hydraulic cylinder 38. The hydraulic cylinder 38 is connected to an actuating member, for example, a release lever of the clutch 18 via a hydraulic pressure transmitting path 40. To detect the position of the piston 36 and/or of the release lever of the clutch 18, a sensor 42 is included, which detects the angle of rotation of the output pinion 32. Changes in the angle of rotation allow a conclusion that linear displacement of the threaded rod 34 has taken place, due to the engagement between the pinion 32 and the threaded rod 34. In order to obtain a reference position, which can be referenced during displacement of the piston 36, an expansion port in the hydraulic cylinder 38 can be crossed in a known manner, causing pressure, during said crossing, to be built up in the hydraulic pressure transmitting path 40, which can be detected through an increase in the torque and/or power consumption of the electric motor 30. Pressure points or stops of the clutch can be used as additional reference positions.
The gears that are arranged on the output shaft 15 of the twin-clutch transmission 10 are moved axially by means of shift forks 46 (see FIG. 1b), which act together with shift fingers 48 that are arranged on a selector shaft 50. For example, one selector shaft 50 can be provided with several shift fingers 48 for actuating all gears that are arranged on the output shaft 15, or two selector shafts 50 can be arranged to actuate the shift forks of those gears that are associated with one of the input shafts, respectively. For each selector shaft 50, two actuators are provided—one that rotates the selector shaft 50 back and forth around its axis in order to engage the gears, and another that displaces the selector shaft 50 axially, in a direction perpendicular to the plane of the paper showing FIG. 1b, so as to select among different switching paths.
The actuators associated with a particular selector shaft 50 have been designated by reference numerals 52 and 54 in FIG. 1a. Position detection can occur in a similar fashion to that shown for the electric motor 30 through increment counters. In order to recognize the absolute position of the selector shaft 50 and/or of the shift finger 48, reference positions must be encountered—for example, stops on a selection path and switching paths or stops that are encountered by the shift forks 46 themselves.
To control the above-mentioned actuators, a control arrangement and/or control device 60 is provided, the inputs of which are connected to various sensors that are useful for controlling the operation of the various actuators, and the outputs of which are connected to the actuators. The control device 60 includes a microprocessor 62 having a program memory 64 and a data memory 66.
The design and the function of the described arrangement are known and will therefore not be explained in detail. During operation in practice, several problems exist with respect to the operating comfort and functional safety of the arrangement. Those problems are solved by means of the present invention.